$ERR_RCBCALL
904
RCB: Call in progress
An attempt was made to modify an RCB argument block when an RCB call that uses the same RCB argument block is being executed. It can occur when using any of these functions: %RCB_CREATE, RCB_DELARG, RCB_DELETE, RCB_INSARG, RCB_SETARG, RCB_SETARGS, RCB_SETFNC, and RX_SETRMTFNC.